#include <kernel/gdt.h>

namespace JLOS::Kernel {
GlobalDescriptorTable::GlobalDescriptorTable()
: nullSegmentSelector(0,0,0),
unusedSegmentSelector(0,0,0),
codeSegmentSelector(0,64*1024*1024,0x9A),
dataSegmentSelector(0,64*1024*1024,0x92)
{
	uint32_t i[2];
	i[1] = (uint32_t)this;
    i[0] = sizeof(GlobalDescriptorTable) << 16;
	
	asm volatile("lgdt (%0)": : "p" (((uint8_t *) i)+2));
}

GlobalDescriptorTable::~GlobalDescriptorTable()
{
}

uint16_t GlobalDescriptorTable::DataSegmentSelector()
{
	return (uint8_t*)&dataSegmentSelector - (uint8_t*)this;
}

uint16_t GlobalDescriptorTable::CodeSegmentSelector()
{
	return (uint8_t*)&codeSegmentSelector - (uint8_t*)this;
}

GlobalDescriptorTable::SegmentDescriptor::SegmentDescriptor(uint32_t base, uint32_t limit, uint8_t flags)
{
	uint8_t* target = (uint8_t*)this;
	if(limit <= 65536) {
		target[6] = 0x40;
	} 
	else {
		if((limit & 0xFFF) != 0xFFF) {
			limit = (limit >>12) -1;
		}
		else {
			limit = limit >>12;
		}
		target[6] = 0xC0;
	}
	target[0] = limit & 0xFF;
	target[1] = (limit >> 8) & 0xFF;
	target[6] |= (limit>> 16) & 0xF;
	
	target[2] = base & 0xFF;
	target[3] = (base >> 8) & 0xFF;
	target[4] = (base >> 16) & 0xFF;
	target[7] = (base >> 24) & 0xFF;
	
	target[5] = flags;
}

uint32_t GlobalDescriptorTable::SegmentDescriptor::Base()
{
	uint8_t *target = (uint8_t*)this;
	uint32_t result = target[7];
	result = (result <<8) + target[4];
	result = (result <<8) + target[3];
	result = (result <<8) + target[2];
	return result;
}

uint32_t GlobalDescriptorTable::SegmentDescriptor::Limit()
{
	uint8_t *target = (uint8_t*)this;
	uint32_t result = target[6] & 0xF;
	result = (result <<8) + target[1];
	result = (result <<8) + target[0];
	
	if((target[6] & 0xC0) == 0xC0) {
		result = (result <<12) | 0xFFF;
	}
	return result;
}
}
